As is well known, in the field of video equipment, for instance, video tape recorders which record still picture data on magnetic recording media such as magnetic tape, floppy disc, etc. and reproduce the recorded data have been developed. However, using this type of conventional video tape recorder, video data to be recorded are frequency modulated and recorded in analog on recording media and therefore, there are limits generated in maintaining the quality of the video data. As a result, picture quality tends to be deteriorated easily.
On the other hand, as a means to solve this problem, video data is digitally coded and recorded on recording media. While this means has merits in that the quality of recorded data can be satisfied without causing deterioration of picture quality, it has a problem in that a substantially longer time is needed than conventional devices when recording/reproducing picture data with sufficiently high quality (e.g., about 400 thousand pixels). This is because the volume and speed of information that can be handled by the recording/reproducing system are limited. For instance, when one pixel is expressed in eight bits of data, 400 thousand pixels will require 3.2 Mega bits of data and when information speed is assumed to be 1.55 Mega bps, 2.07 seconds will be needed for recording or reproducing one picture.
On such a video tape recorder requiring much time to record or reproduce one picture, it becomes difficult to realize a so-called quick turn-over function to look for desired pictures by retrieving pictures successively at high speed such as, for example, turning over pages of a book.
So, a video tape recorder that is capable of realizing the quick turn-over function by displaying picture data reproduced from a recording medium while thinning them out (or decimating them) has been proposed. FIG. 1 shows a conventional video tape recorder which has been proposed in Japanese Patent Application; Toku-Gan-Sho 62-330501 filed on Dec. 26, 1987 (not published). In FIG. 1, an input terminal 20 is provided for receiving digitized picture data. The picture data applied to the input terminal 20 are stored in a recording data memory 22 and then are read out in a prescribed arrangement by a first address controller 24.
Here, it is assumed that the portion shown by "A" in FIG. 2 is one digitally expressed complete picture and each pixel composing this one complete picture A is one picture element. The total pixels composing the one complete picture A are sampled half in the longitudinal (vertical) direction and half in the lateral (horizontal) direction, respectively, and divided into four sub-pictures. That is, picture A is divided into a first sub-picture having a group of pixels [1], a second sub-picture having a group of pixels [3], a third sub-picture having a group of pixels [3], and a fourth sub-picture having a group of pixels [4].
Picture data corresponding to these first to fourth sub-pictures are orderly arranged and recorded, as shown in FIG. 3, when, for instance, they are recorded on a magnetic tape 26 (see FIG. 1) by a helical scanning system. Therefore, the first address controller 24 controls the reading operation of the picture data stored in the recording data memory 22 in the order as shown in FIG. 3. That is, the first address controller 24 controls the recording data memory 22 in such a way as to read out the pixels [1] first and then, the pixels [2], [3] and [4] in that order.
The picture data which are thus output from the data arrangement converter 24 are then modulated for recording in a recording signal processor 28. The picture data thus modulated are alternately supplied to magnetic heads 30a, 30b which are supported by a rotary drum 32 via a record/playback mode selector (referred to as R/P mode selector hereafter) 34 after they are combined with parity bits for error correction.
Picture data obtained by reproducing magnetic tape 26 with the magnetic heads 30a, 30b are supplied to a reproduced signal processor 36 via the R/P mode selector 34 and undergo demodulation, error correction, and other correction processes. Thereafter, the picture data which are output from the reproduced signal processor 36 are written into a reproduced data memory 38. The reproduced data memory 38 is selectively coupled to either a second address controller 40 or a third address controller 42 through a display mode selector 44.
When reproduction of one complete picture is demanded, the second address controller 40 is selected by the display mode selector 44. Further, when reproducing one complete picture, the first through the fourth sub-picture signals recorded on the magnetic tape 26 are all read out by the magnetic heads 30a, 30b. Then, the second address controller 40 controls the reproduced data memory 38 to write therein all the picture data that are output from the reproduced signal processor 36. Therefore, the picture data of the first through fourth sub-pictures are written into the reproduced data memory 38 in such a way that the pixels are arranged as shown in FIG. 2.
Thereafter, the picture data are successively read out of the reproduced data memory 38 at a fixed rate and are supplied to a picture display device 46 through a picture processor 48, a digital/analog converter (referred to as D/A converter hereafter) 50, and a video encoder 52. Thus, one complete picture is displayed.
On the other hand, in the quick turn-over mode, the third address controller 42 is selected. Further, during the quick turn-over operation, the picture data record portion of only the first sub-picture is read from the the magnetic tape 26 by the magnetic heads and second through fourth sub-pictures are skipped.
Next, the third address controller 42 controls the reproduced data memory 38 to write therein the picture data of the first sub-picture which are output from the reproduced signal processor 36 in such a way that the pixels are arranged, as shown in pixel position [I] of FIG. 2. Further, nothing is recorded on the pixel positions [2], [3] and [4] where the picture data of the second through the fourth sub-pictures are to be written.
Thereafter, the picture data stored in the reproduced data memory 38 are read out at a fixed rate and are finally supplied to the picture display device 46 for display at the time of quick turn-over. In this case, as the picture display is carried out on the basis of the picture data of the first sub-picture, the picture quality itself may become rough but the purpose of the quick turn-over is achieved smoothly.
Therefore, as it has been so designed that only this picture data record portion of the first sub-picture of the magnetic tape 26 is reproduced and those of the second through the fourth sub-pictures are skipped during the quick turn-over, it becomes possible to perform the high-speed retrieval.
However, on such a conventional video tape recorder as mentioned above, the retrieval speed is fixed at a single speed and other speeds are not selectable. Further, only the picture data of the first sub-picture are read from the magnetic tape 26, skipping the picture data of the second through the fourth sub-pictures during the quick turn-over operation. Furthermore, a problem arises in which only a quarter of the sub-picture divided into four can be displayed all the time, especially in multiple picture display.
As described above, in retrieving desired pictures through the quick turn-over operation on a conventional video tape recorder, a defect exists such that the picture retrieval speed is fixed at one speed only while one complete picture is recorded after being divided into four sub-pictures during the reproduction through the quick turn-over operation, only the first sub-picture is reproduced, skipping other sub-pictures, and after rearranging the pixels of the reproduced first sub-picture in one complete picture area, only one picture consisting of this first sub-picture data only are displayed. Furthermore, a defect exists such that as the first through the fourth sub-picture data are recorded in order on a magnetic tape as described above, the fourth division sub-picture can be displayed only during the multiple display and the degree of freedom of the multiple display is restricted.